Telephone system.



A. H. DYSON.

TELEPHONE SYSTEM. APPLICATION TILED APILM, 1902.

1,035,172 Patented Aug. 13, 1912.

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UNITED STATES PATENT OFFICE.

ALFRED H. DYSON, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO STROMBERG-CARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

To all whom it may concern:

Be it known that I, ALFRED H. DYSON, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Telephone Systems, of which. the following is a specification.

My invention relates to telephone systems of that class in which the circuit connections are such that any subscriber of one exchange may be connected up for conversation with any subscriber of another exchange. Telephone systems of this character are usually known as trunking systems, the connections between the two exchanges consisting of a number of lines, commonly termed trunk lines. With this arrangement, a subscriber of one exchange can send in a call asking for connection with a subscriber of another exchange, and the connection between the two subscribers can then be made through the medium of one of the trunk lines between the two exchanges, and also by means of the operators cord-circuits at the two exchanges.

There are certain telephone systems in which the current for operating the subscribers transmitters is supplied from local batteries located at the substations, while the current for operating the calling and supervisory signals at the central station is supplied from a battery associated with the switch-board apparatus. In other words, only the current necessary for signaling purposes is supplied from a central source, while the current for talking purposes is supplied from the local batteries atthe substations. An exchange operating on this principle is ordinarily known as abentralized call exchange. There is, however, another type of telephone system in which the current, both for talking and signaling purposes, is supplied from a common or centralizedbattery located at the exchange or central station. With this arrangement, the current is supplied to the subscribers lines from a central source, both for-operating the subscribers transmitters, and also for operating the line and supervisory signals involved in the switchboard apparatus. An exchange operating onthis principle is known as a common battery exchange.

Now one of the principal objects of my Specification of Letters Patent.

Patented An". 13, 1912.

Application filed April 14, 1902. Serial No. 102,715.

invention is to provide a simple and highly eflicient construction and circuit arrangement whereby trunking may be successfully carried on between two exchanges, one of the centralized call type, and the other of the common battery type.

A special object is to provide an improved circuit arrangement whereby connection may be made from a centralized call exchange to a common battery exchange.

Another object is to provide an improved circuit arrangement whereby the originating operator at a central call exchange may have complete control and supervision of the connections and dis-connections between an exchange of this character and an exchange operating on the common battery principle.

A further object is to provide suitable and improved circuit arrangements whereby connection may be made from a centralized call exchange equipped with a particular form of switchboard apparatus to a common battery exchange also equipped with a particular form of switchboard apparatus.

In addition, it is also an object to provide certain details and features of improvement tending to increase the general efliciency and serviceability of a telephone system of this character.

The accompanying drawing is a diagram illustrating a trunking telephone system embodying the principles of my invention. In this diagram, a local battery substation is shown connected up with a centralized call exchange, and a common battery substation telephone set is shown suitably connected up with a common battery exchange. It will also be seen that a single trunk-line is shown extending between the two exchanges. It will be readily understood that only such instruments, devices and circuit connections are illustrated as are necessary to a full understanding of the invention.

In installing telephone systems it often becomes desirable and practically necessary to provide suitable circuit arrangements whereby a subscriber of one exchange may be connected up for conversation with a subscriber of another exchange. It often happens that the two exchanges are of ditlerent types-that is, that one is a centralized call exchange, while the other is a full common battery exchange. In such case, it is desirable that the trunking between the two exchanges be carried on without materially changing the mode of operation of the two exchanges, and without making any changes in the arrangement of the subscribers lines and talking sets. In other words, it is desirable that the methods of operation of each exchange be retained, so far as the connecting and disconnecting of subscribers of one exchange is concerned. At the same time, it is desirable that the originating operator, or operator at whose exchange the call originates, have complete control and supervision of the trunk connections between the two exchanges. In view of these conditions and requirements, my improved trunking circuit connections are designed to afford a satisfactory method of trunking between a centralized call and a common battery exchange, and particularly in connection with two exchanges having the particular form of construction of switchboard apparatus herein shown and described.

As illustrated, the system comprises a substation A having a microphone transmitter a supplied with current from a local battery (4, and a substation 13, having a microphone transmitter b supplied with current from the exchange or central station. The substation A is shown connected with the entralized call exchange indicated by C, while the substation B is illustrated as being counected with the common battery exchange indicated by D. The two exchanges are,

it will be seen, connected by a suitable trunkline E. It will be understood, however, that in a system of this character any desired number of trunk-lines can be employed between the two exchanges.

Now assuming that the subscriber at substation A desires connection with the sub scriber at substation B, the circuit connections and operations which then take place are as follows: The removal of the receiver a from the hook-switch at substation A serves to complete a circuit from the battery F, through the battery lead 1, through the coil of the line relay 2, through the conductor 8 and the contact-point 4, thence through the armature 5 and the line conductor 6, through the said receiver a and the secondary 7 of the induction coil, through the contact-point 8 and the hookswitch 9, thence through the other line con ductor 10, through the armature 11 and con tact-point 12, through conductor 13, and thence through the ground or common connections 14 and 15 to said battery. The current flowing through this completed line circuit energizes the said relay 2, causing it to attract its armature. The said armature when attracted completes a short local circuit from the battery F through the conductor 1 and the coil of the relay 2', through the conductor 3 and contact-point 4,

through the armature 5 and conductor 16, through the linelamp 17, through the con tact-point 18 and the armature 19, through the conductor 20 and the armature 11,

thence through contact-point 12 and conductor 13, and through the ground or common connections 14 and 15 to said battery. Thus it will be seen that the relay 2, in at tracting its armature, closes a local circuit through itself, by reason of which arrange-- ment it continues to attract its armature until the local circuit is broken, regardless of whether the subscriber has hung up the receiver or not. In other words, the relay 2 is connected and arranged to serve as part of both line and local circuits. The flow of current through this local circuit causes the lamp 17 to glow, thus attracting the attention of the operator and indicating that the subscriber at substation A desires to give an order for connection. The originating operator at exchange C, or the exchange at which the call originates, then inserts the answering plug of the cord-circuit in the jack corresponding to the calling subscribers line. This, it will be seen, operates to complete another local circuit from the battery F, through conductors 1 and 21, through the coil of the cut-out relay 22, thence through the jack contacts 23 and 24, it being observed that the insertion of the plug in the jack has closed these contacts, and thence through the ground or common connections 25 and 15, to said battery. The flow of current through this local circuit energizes the cut-out-relay 22, causing it to attract its two armatures 5 and 11. Consequently, the insertion of the plug operates to automatically disconnect the battery and line relay from the line, and the latter being deenergized, the line lamp is extinguished or restored. After thus inserting the plug and automatically restoring the line signal, the originating operator then presses the usual listening key, so as to establish connection between the line and the operators talking set, which, it will be understood, may

consist of the transmitter X and the receiver X. The energizing of the cut-out relay having established connection betweenthe jack and the line by reason of the armatures 5 and 11 having moved into contact with the contact-points 26 and. 27, the originating operator can now receive an order for connection from the calling subscriber. It will be readily understood that the operators talking set can be of any suitable or approved form. After receiving the order for connection, the originating operator then presses the key 9' in the operators private order line G, it being observed that this order line is permanently connected with the trunking operators talking set at the common battery exchange. D, and is, by reason of the key 9, normally disconnected from the operators talking set at the centralized call exchange C. The trunking operators talking set, consisting of the transmitter Y and the receiver Y, being thus connected to the originating operators talking set, the latter can then advise the trunking operator as to the character of the connection desired. Upon learning the number of the substation desired, the trunking operator then immediately assigns a certain idle trunk-line between the two exchanges, which line is, in this case, assumed to be the trunk-line E. The originating operator then immediately plugs into the trunk-jack connected with this trunk-line, and in so doing completes a local circuit from the battery F, through the conductor 28 and the coil of the supervisory relay 29 associated with the said jack, through the conductor 30, through the trunk-jack contacts 31 and 32, it being observed that these two contacts have been brought together by reason of the insertion of the originating operators calling plug, and, finally, through the ground connections 33 and to said battery. The insertion of the plug in the trunk-jack also operates to complete a circuit from the battery F through the conductor 34, and the lower coil of the relay 35, thence through the sleeve strand and the sleeve of the plug, through the spring 41 of the trunk-j ack, through the conductor 42, impedance coil 43, conductor 44, contact point 45 and armature 46, and thence through the ground or common connections 47 and 15, to said battery. The completion of this grounded circuit serves to energize the relay 35, causing it to attract its armature. The said armature when attracted completes a short local circuit from the battery F, through conductor 34, supervisory lamp 48, thence through the contact-point 50 and the armature 51, and, finally, through the ground or common connections 52 and 15 to said battery. The current flowing through this local circuit causes the supervisory lamp 48 to glow, indicating that no connection has been made with the called subscriber. This lamp, as will be seen, continues to glow until the subscriber at substation B answers the call.

Now, after making one of the usual tests, so as to ascertain whether or not the line of substation B is busy, the trunking operator then, in case the line is not busy, inserts the plug of the trunking cord-circuit in a jack corresponding to the line of substation B. After thus inserting the cord-circuit plug in the jack connected with the called subscribers line, the trunking operator then projects ringing current on to the line in any suitable manner, as, for example, by pressing the ringing key Z, so as to throw current on to the line from the generator U. The generator current thus projected on to the called subscribers line rings the bell b at substation B. Furthermore, the insertion of the trunking cord-circuit plug in the called subscribers spring jack, serves to complete a local circuit from the battery F, through the conductor 53 and the coil of supervisory relay 54, thence through the conductor and the contact-point 56, through the spring 57 of the usual listening key, thence through conductor 58 and the contact-point 59, through the ringing key Z, through the sleeve contact (50 of the trunking cord-circuit plug, thence through the testing ring or thimble 61 of the called subscribe1"s jack, through the conductors 62 and (53, through the impedance coil 64, thence through the conductor 65 to said battery. This energives the relay 54, causing it to attract its armature. The said armature, as will be seen, continues to be attracted and held against its associated contact until the plug of the trunking operators cord-circuit is withdrawn from the called subscribcrs jack.

hen the called subscriber responds to the call, that is to say, when the subscriber removes the receiver b from the hookswitch, a line circuit is completed from the battery F, through the conductor 66, through the impedance coil 67, through the conductors 68 and (39, thence through the ring contact spring 70 of the called subscribers jack, thence through the ring contact 71 of the plug, through the conductor 72, through the coil of the supervisory relay 73, through the cord-strand 74, through the plug tip 7 5, thence throilgh the tip spring 76 of said jack, through the line conductor 77 and the subscribers transmitter 5, through the hook-switch 78 and the primary 7 9 of the induction coil, thence through the other line conductor 80, through the conductor 62, and the impedance coil (34, thence through the conductor 65, to said battery. The current takes this path, it will be seen, by reason of the coil of supervisory relay 73 being of lower resistance than the line relay R, which is also in the line circuit, consequently, the line relay R does not become energized when the called subscriber answers the call, and in this way the said subscriber responds without causing the line lamp 7' to glow. In other words, the coil of supervisory relay 73 constitutes a relatively low resistance shunt adapted to be placed in the line to short-circuit the line relay R. The current flowing through this supervisory relay 73 energizes it and causes it to attract its armature 46. Now as this armature, aswill be seen from the previous description of the connections, constitutes part of the energizing circuit of the supervisory relay 35 in the originating operators cordcircuit, it follows that when attracted this armature serves to break or open the circuit of relay 35, thereby causing the latter to become deenergized,and to release its armature 51. This armature 51 in moving away from contact 50 breaks or opens the local circuit in which the supervisory lamp 48 is included, and in this way the called subscriber in answering a call closes a line circuit which energizes the relay 73, and the energizing of this relay in turn opens or breaks the grounded trunk line circuit, thereby deenergizing the originating operators supervisory relay and restoring or extinguishing the supervisory lamp 48. In this way, the originating operator is enabled to supervise the connections and to know when the called subscriber responds to the call.

The trunking operators cord-circuit is preferably provided with condensers (Z located in each talking strand, and the lower limb of the trunk line is preferably provided with. a condenser 6, located preferably just outside of the trunk ack.

After finishing their conversation, the subscribers in hanging up their receivers automatically signal for disconnection. For example, the subscriber at substation A, in hanging up receiver a completes a grounded line circuit from the battery F, through the conductor 34, through the coil of supervisory relay 35, thence through the conductor 81 and the talking strand 82 of the cord-circuit, thence through the plug tip 813 and the jack spring 84, through the 0011- taet-point 26 and the armature 11, through relay 93 is energized sufficiently to attract the line conductor 10 and the hook-switch 9, and thence through the contact-point 85 and the conductor 86, through the subscribers bell 87, and, finally, through the ground connections 88 and 15 to said battery. This, it will be seen, again energizes the relay causing it to attract its arma ture and close the local circuit including the lamp 48. This lamp then glows or lights up, and in so doing indicates that the sub scribers are ready to be disconnected. The originating operator then withdraws both plugs from the jacks-that is to say, both from the calling subscribers jack and the trunk jack, so as to disconnect the two lines: It will also be seen, however, that the hanging up of the receiver Z2 at substation B opens the line circuit, thereby deenergizing the line relay 73, and allowing the latter to release its armature. The said armature, when released, immediately makes contact- -with the resting contact-point 45, thereby again closing the grounded trunk-line circuit including the coil of relay 35. In this way, the opening of the called subscribers line by the depression of the hookswitch also operates to automatically energize the relay 35, and to cause the lamp 48 to glow. In other words, either subscriber can, by hanging up the receiver, energize the relay 35 and operate the supervisory or clearingout signal associated with the originating operators cord-circuit. The originating operator, observing this signal, then, as stated, withdraws both plugs from the jacks. It will be seen, however, that during all this time the trunking operator knows nothing about the condition of the subscribers lines-that is to say, does not know whether or not the two subscribers have finished conversation. Consequently, the trunking operator does not withdraw the plug of the trunk cord-circuit from the jack of the subscribers line until the proper signal is received from the originating operator. This signal is given by the originating operator in withdrawing the plug from the trunk jack, it being observed that as soon as this is done the relay 29 is deenergized, and'its armature thereby released. The said armature, when released, completes a grounded circuit from the common battery F, through the conductor 89' and the armature 90, it being observed that the latter is at-- .tracted by the magnet of relay 54E, thence through the contact-point 91, and the conductor 92, through the coil of relay 93, and

the conductor 94, through the cord-strand 95 and the lower limb of trunk-lineE, thence through the conductor 96 and the contactpoint 97, through the armature 98 of relay '29, thence through the conductor 99, and, finally, through the ground connect-ions 100 and 101 to said battery. Thus included in the closed grounded trunk-line circuit, the

its armature. The said armature, when attracted, closes a local circuit, from the batitery F, through the conductor 102, through the supervisory lamp 103, thence through the contact-point 104k and the armature 105, and through the ground or common connections 106 and 101 to said battery. The flow of current through this local circuit causes the' lamp 103 to glow, and the trunking operator observing this signal then withdraws the plug of the trunking cord-circuit from the called subscribers spring jack. as explained, the trunking operator acts en- Thus,

tirely on the instructions given by the originatmg operator, and does not disconnect until at proper signal is-received from the latter. It will also be seen that though a call originates at the centralized call exchange,

the connections between the two exchan es are made in a satisfactory and eflicient manner, and without interfering with the ap- 1 proved or established methods of operation.

Furthermore, these advantages are obtained in a trunking telephone system involving a centralized call exchange having jacks nor- ;mally dlsconnected from the lmes, andv in- 1 volving a common battery exchange having cord-circuit shunts adapted to be placed in the lines for the purpose of short-circuiting or shunting out the line relays.

It will be seen that the supervisory relay 35 is double-wound and connected at a point between the two coils, with the nongroundecl pole of the battery. In this case, the upper coil is used by the calling subscriber, as he hangs up his telephone, for closing the circuit of the supervisory lamp. In a similar way, and through the medium of the short-circuiting relay 73, the called subscriber can close a grounded trunk-line circuit including the lower coil of the relay 35. Thus the two coils balance each other, so as to produce a quieting effect on the talking circuit. In addition, each coil is, with the arrangement shown, adapted to serve as part of the supervisory signaling apparatus. It will be understood, of course, that the sleeve contacts of the plugs connected with the originating operators cord circuit do not make contact with the thimbles or testing rings of the jacks,that is, when the plugs are fully inserted. In other words, the lower or sleeve strand of the cord circuit C is not connected through the plug sleeves with the said testing rings when the plugs are inserted. Consequently, these testing rings are used for testing purposes only, the test being made by touching the tip of the plug to the testing ring of the jack of the line being tested. When this is done, and if the line is busy or in use, current flows from ground through the testing ring, through the tip of the plug, through the upper coil of the relay 35, and thence to the non-grounded pole of the battery. The supervisory relay being thus energized, the supervisory lamp is lighted momentarily, thus giving a visual busy test.

I claim as my invention- 1. In a trunking telephone system, the combination of a centralized call exchange, a common battery exchange, a trunk-line extending between the two exchanges, a calling subscribers line suitably connected with the centralized call exchange, a subscribers telephone set including a local battery and microphone transmitter, a called subscribcrs line suitably connected with the connnon battery exchange, a subscribers telephone set suitably connected with said called subscribers line, said last mentioned telephone set including a microphone transmitter connected and arranged to receive current from the common source at the common battery exchange, means whereby an operator may produce a call signal at any called subscribers station, an order line extending between originating and trunking operators, and means by which the originating operator supervises the connection.

2. In a trunking telephone system, the combination of a centralized call exchange provided with an originating operators cord-circuit, a common battery exchange provided with a trunking operators cordcircuit, a trunk line extending between the two exchanges, a local battery substation suitably connected with said centralized call exchange, a common battery substation suitably connected with said common battery exchange, means whereby an operator may produce a call signal at any called subscribers station, an order line extending be tween originating and trunking operators, and means by which the originating operator supervises the connection.

3. In a trunking telephone system, the combination of a calling subscribers line, a calling subscribers telephone set including a microphone transmitter and a local battery, an originating operators cord-circuit, a battery associated with said cord-circuit and connected and arranged to supply current to the calling subscribers line for signaling purposes only, a trunking operators cord-circuit, a trunk line connected and arranged to serve as medium of connection between the two cord-circuits, a called subscribers line terminating at the exchange at which the trunking operators cord-circuit is located, line signal apparatus associated with the called subscribers line, a subscribers telephone set suitably connected with the called subscribers line and involving a microphone transmitter, and a common battery associated with the trunking operators cord-circuit and connected and arranged to supply current to the called subscribers line for both talking and signaling purposes.

l. In a trunking telephone system, the combination of switch-board apparatus involving suitable line terminals and line or calling signals, a battery associated therewith and connected and arranged to supply current to said lines for signaling purposes, local batteries for talking purposes, a trunk line terminating in a trunk-jack located at the exchange having said switchboard ap paratus, suitable switch-board apparatus connected and associated with the other end of said trunk line, said last mentioned switchboard apparatus involving suitable line terminals and line or calling signals, a common battery connected and arranged to supply current to the lines terminating at said last mentioned switchboard apparatus, for both talking and signaling purposes, means whereby an operator may produce a call signal at any called subscribers station, an order line extending between originating and trunking operators, and means by which the originating operator supervises the connection.

5. In a trunking telephone system, the combination of a calling subscribers line, a jack normally disconnected from said line, an originating operators cord-circuit associated with said jack, line signal apparatus associated with the calling subscribers line, a cut out relay for restoring the line signal apparatus and establishing connection be- 2 tween the line and the said jack, a battery associated with the originating operators, cord-circuit and connected and arranged to' supply current for both energizing said cut-out relay and operating the said line signal apparatus, a trunk jack associated with I the said originating operators cord-circuit, a trunk-line having one end permanently connected with said trunk-jack, a trunking operators cord-circuit permanently connect ed with the other end of said trunk-line, a spring jack associated with said trunking .operators cord-circuit, a called subscribers line permanently connected with said last mentioned jack, a line relay associated with the called subscribers line, the said trunking operators cord-circuit being provided with a low resistance supervisory relay adapted to be placed in the line to shortcircuit said line relay, and a battery associated with the trunking operators cordcircuit and suitably connected for supplying current to the called subscribers line for talking purposes, and also for the purpose of energizing the said line and supervisory relay.

6. In a trunking telephone system, the combination of two exchanges, a trunk line extending between the two exchanges, a supervisory relay and a battery at one exchange, a plug switch for closing a local circuit including said battery and relay, a grounded circuit including one limb of said trunk line, said circuit having a normally closed switch-point controlled by said supervisory relay, a supervisory relay and a normally open switch-point in said grounded circuit at the other exchange, a supervisory relay for controlling said normally open switch-point, a battery permanently connected with said third supervisory relay, said battery being grounded to form part of the said grounded circuit including one limb of the trunk line, a plug switch for closing or completing a circuit through said third supervisory relay, so as to close said normally open switch-point in the grounded trunk-line circuit, a supervisory lamp located in a local circuit including said last mentioned battery, and a normally open switch-point controlled by the relay located in the grounded trunk-line circuit, this relay in the trunk-line circuit being energized and the said lamp being caused to glow when the first mentioned relay is deenergized.

7 In a trunking telephone system, the combination of a trunk line connected at one end with a trunk-jack, an originating operators supervisory relay associated with said jack, an originating operators supervisory lamp associated with the said relay, a normally open switch-point controlled by the said supervisory relay, a trunking operators supervisory relay, a grounded trunkline circuit including said originating operators supervisory relay, a normally closed switch-point in said grounded circuit c0ntrolled by the trunking operators supervisory relay, a battery permanently connected with said originating operators supervisory relay and also arranged to supply current to said lamp, a second grounded circuit including the other limb of said trunk line, normally open and normally closed switchpoints in said grounded circuit, a relay under the control of the trunking operator and arranged to control the said normally open switch-point, a trunking operators supervisory lamp, a battery permanently connected with said lamp, a normally open switch-point in the circuit of said trunking operato-rs supervisory lamp, and a relay located in said second grounded circuit and arranged to control a normally open switch-point in the circuit of the trunking operators supervisory lamp.

8. In a trunking telephone system, the combination of a calling subscribers line, a normally open connection across the terminals of said line, a line relay connected and arranged to close said normally open connection, a battery connected to supply current through said relay to said line, a line lamp, the local circuit of said line lamp including said relay and normally open connection and also including said battery, the coil of said relay thereby being adapted to serve as part of both line and local circuits, an originating operators cord-circuit, a trunking operators cord-circuit adapted to serve as medium of connection between the two cord-circuits, supervisory signal apparatus associated with the trunking operators cord-circuit, a plug switch and suitable connections whereby the originating operator has control of the said supervisory signal apparatus, a called subsoribers line, a line relay associated with said called subscribers line, the trunking operators cord-circuit being provided with a supervisory relay of relatively low resistance adapted to be placed in the line to short-circuit said last mentioned relay, supervisory signal apparatus associated with the originating operators cord-circuit, and suitable connections and circuit-changing devices whereby said last mentioned supervisory apparatus may be controlled or brought into action either by the closing of a grounded line circuit including one limb of the calling subscribers line, or by the opening of the called subscribers line circuit.

9. In a trunkingtelephonesystem, the com-. bination of a calling subscribers line, a called subscribers line, an originating operators supervisory signal, connections and circuit changing means whereby said signal may be displayed by closing a grounded circuit including one limb of the calling subscribers line, suitable connections and circuit-changing means whereby said signal may be displayed by the opening of the called subscribers line circuit, line signal apparatus associated with the calling subscribers line, a centralized call battery connected to supply current to the calling subscribers line for signaling purposes only, line signal apparatus associated with the called subscribers line, a second battery con nected and arranged to supply current to the called subscribers line, for both talking and signaling purposes, a trunking operators supervisory lamp, and suitable connections and circuit closing devices whereby the said last mentioned lamp may be caused to glow by the closing of a grounded circuit including one limb of a trunk-line.

10. In a trunking telephone system, the combination of a calling subscribers telephone set including a microphone transmitter and local battery and also including a grounded bell connected by a hook-switch with one side of the line, a called subscribers telephone set including a microphone trans mitter and a hook-switch for closing the line circuit, suitable line signal apparatus associated with the calling subscribers line, a centralized call battery connected and arranged t'or supplying current to the calling subscribers line for the purpose of ope "ating said line signal apparatus, an originating operators supervisory relay permanently connected with said battery, suitable connections whereby said relay may be energized by the closing of a grounded line circuit including said grounded bell, suitable line signal apparatus associated with the called subscribers line, a battery connected and arranged to supply current to the called subscribers line for talking purposes and also for the purpose of operating the said last-mentioned line signal apparatus, a suitable trln'ik-line, a normally open grounded circuit including one limb of said trunlo line and also including the originating operators suppervisory relay, a trunking operators supervisory relay connected and arranged to be deiinergized when the called subscribers line is open, a normally open switch-point in the grounded circuit controlled by said trunking operators supervisory relay, a trunking o-perators supervisory signal, and suitable connections and circuit-closing devices whereby the originating operator may close a grounded circuit including the other limb of said trunk line, and whereby the closing of this second grounded trunk-line circuit will cause the said trunking operators supervisory signal to be displayed.

11. In a trunking telephone system, the combination of a centralized call exchange, a common battery exchange, a trunk-line extending between the two exchanges, a trunkjack connected with the trunk line at the centralized call exchange, a trunking operators cord-circuit connected with the trunkline at the connnon battery exchange, a condenser in one limb of the trunk-line at the jack end thereof, suitable supervisory signal apparatus associated with the trunking operators cord-circuit, an orginating operators cord-circuit provided with a plug adapted for insertion in said jack, suit-- able connections and circuit closing devices whereby the insertion of the plug in said jack maintains the said supervisory signal apparatus in an operative condition, and whereby the withdrawal of the plug from said jack causes the operation of said apparatus and the display of the supervisory signal, means whereby an operator may produce a call signal at any called subscribers station, an ordcr'line extending between originating and trunking operators, and means by which the originating operator supervises the connection and receives a signal, over a ground circuit, when the called subscriber hangs up the receiver.

12. In a trunking telephone system, the combination of a centralized call. exchange, a calling subscribcfis line connected with said exchange, a common battery exchange, a called subscribers line connected with said lastunentioned exchange, a trunk-line ex tending between the two exchanges, a trunkjack connected with the trunk-line at the centralized call exchange, a su 'iervisory signal apparatus located at the common battery exchange, a local circuit including the centralized call battery at the first mentioned exchange, a relay in said local circuit, said local circuit also including a pair of normally separated contacts of said jack, a grounded circuit including one limb oi the trunk-line, a normally closed switclrpoint in said grounded circuit controlled by said relay, an originating operators cord-circuit plug adapted for insertion in said jack, the plug when inserted in the jack causing the said normally separated contacts to be broliight together, so as to energize said relay and open said normally closed switchpoint in the grounded cirmit, and suitable connections whereby the withdrawal of the plug and the consequent closing of said grounded circuit causes the operation of said supervisory signal apparatus and the display of the supervisory signal.

1.3. In a trunking telephone system, the combination of a calling subscribers line, an originating operators cord circuit, a trunking line, a condenser in a limb thereof at the jack end, a trunking operators cord circuit, a called subscribcrs line, together with line and supervisory signaling apparatus associated with the two lines and the two cord circuits, batteries at the central stations for supplying current to the line circuits to operate the line and supervisory signals, means whereby an operator may produce a call signal at any subscribers station, an order line extending between originating and trunking operators, and means by which the originating operator supervises the connection and receives a signal, over a ground circuit, when the called subscriber hangs up the receiver.

14. In a trunking telephone system, the combination of calling and called subscribers lines, a trunking line, a plurality of two wire cord circuits for connect-ing the trunking lines with the subscribers lines, a battery associated with one cord circuit and permanently connected with one of the subscribers lines, and a battery associated with the other cord circuit and normally connected with the other subscribers line and a cut-off relay to disconnect said battery from the latter line during conversation.

15. A trunking telephone system comprising a trunk line, calling and called subscribers lines, means for connecting the trunk line with the subscribers lines, a centralized battery for furnishing current to the trunk line for signaling purposes, means whereby an operator may produce a call signal at any called subscribers station, an order line extending between originating and trunking operators, and means by which the originating operator supervises the connection and receives a signal when the called subscriber hangs up the receiver.

16. In a telephone system, a subscribers line, a ack normally disconnected therefrom, means for trunking said line into connection with another line, means for giving a disconnect signal by grounding the first mentioned line at the subscribers station, and a cut-off relay actuated over a circuit independent of the talking circuit of the line.

17. In a telephone system, a subscribers line, a jack normally disconnected there from, means including originating and trunking operators cordcircuits for trunking said line into connection with some other line, a supervisory signal, and means for operating said signal by either grounding the first mentioned line or the operators cord circuit.

18. In a telephone system, a calling subscribers line, a jack normally disconnected therefrom, means for automatically connecting the jack with the line when the originating operator answers the call, a trunking operators cord circuit, a supervisory apparatus for the originating operator, and means for causing said supervisory apparatus to give a disconnect signal upon the grounding of either the calling telephone line or the trunking line leading to the trunking operators cord circuit.

19. In a telephone system, a calling telephone line, a jack normally disconnected therefrom, means including an originators cord circuit and a trunking operators cord circuit for trunking the line into connection with some other line, a line signal for the calling telephone line, a cut-ofi relay, means for energizing the cut ofi' relay over a local circuit independent of the talking circuit to retire the line signal and connect the jack with the calling line when the originating operator answers the call, and means, including a metallic circuit, by which the called subscriber gives a disconnect signal.

20. In a telephone system, a pair of telephone lines, a line relay for one line temporarily disconnected therefrom, and a line relay for the other line temporarily shunted during conversation, a trunk line for con necting said lines for conversation and means associated therewith for shunting the latter line relay.

Signed by me at Chicago, Cook county, Illinois, this 12th day of April 1902.

ALFRED I-I. DYSON.

Witnesses:

ARTHUR F. DURAND, HARRY P. ,BAUMGARTNER.

Copies of this :patent may be obtained for five cents each, by addressing the Commissioner of Patents. Washington. D. C. 

